The use of high pressure processing (“HPP”) for microbial inactivation is known in the literature. (See, for example, Ohio State University Extension Fact Sheet, “High Pressure Processing Fact Sheet for Food Processors”, ohioline.osu.edu/fse-fact/0001.html).
In addition to the literature, various patent publications deal with high-pressure processing. Generally speaking, those patent publications are concerned with processes having both high-pressure and high temperature processing steps. Furthermore, high-pressure processes for fruit have not been identified.
For example, U.S. Pat. No. 6,033,701, issued to Hirsch discloses a process to sterilize foods, prevent the ripening of some fruits and vegetables, and allow preservation of food components. The various examples described by Hirsch involved application of a low pressure of 25,000 psi applied over a long period of 5-8 days. The examples show successful pasteurization of several fruits, such as apricots, black grapes, blueberries, kiwi, mango, peaches, and pears as well as the successful pasteurization of multiple vegetables. The method described is a batch process. According to Hirsch, whole, peeled or cut fruit may be surrounded by a solution of vitamin C, citric acid, or both to prevent or reduce discoloration. The low pressure process did not work for white grapes, beef, and emu meat; however, after the initial treatment, preservation was obtained by then surrounding the product with yogurt and re-pressurizing it. This multi-step process using yogurt did not work on green grapes, which still turned brown.
Published U.S. Appl'n. No. 2007/0237865 of Love et al. concerns a high pressure process for processing foods after packaging to extend shelf life and eliminate bacteria. Suitable food products include protein, vegetables, sauces, and starches, as well as seafood. In the process, the food product is prepared by grilling, baking frying boiling, steaming or marinating. Then the food is vacuum sealed before being pressurized. Pressure in the range of 25,000 psi to 120,000 psi is applied for a duration of 1 to 30 minutes.
Published U.S. Appl'n. No. 2004/0191382 of Cooper et al. involves sterilization of vegetables, particularly potatoes having a pH of at least 4.5. The exemplary vegetable (potato) is precooked before being packaged, and prior to the pressurization process. In addition, the application describes a multiple-step pressurization process, with a pressure of at least 50,000 psi being applied in total for less than 20 minutes. A single-step process is disclosed, where preheated products (60 to 90° C.) are subjected to pressures of at least 100,000 psi for at least 5 minutes.
U.S. Pat. No. 6,207,215 to Wilson et al. concerns a method for sterilizing and processing foods, particularly low-acid (i.e., pH 4.6) canned foods. Suitable foods include, for example, pet foods, main meals, sauces, soups, stews, vegetables, beverages, and juices. Wilson et al. use a combination of high pressure and high temperature to sterilize. The pressures listed range from at least 75,000 psi to less than 250,000 psi. Raw meat is used in the examples. According to Wilson et al. high acid foods (pH<4.6) are not prone to the growth of pathogens
Published U.S. Appl'n. No. 2005/0112252 to Tewari relates to a process for extending product shelf-life by inactivating microorganisms. A food product is placed in a flexible, sealed, vacuumed container, which is then placed in a processor where the temperature of a pressurizing medium is lowered to a minimum of 10 degrees Fahrenheit. Pressure of the medium is adjusted to be between 10,000 and 130,000 psi. The pressure is held for a minimum of 0.1 seconds. Examples applied the process to salad dressing, salsa, black pepper, and fresh fruits, specifically sliced cantaloupe and peaches. After the food is placed in the container and sealed, the container may be surrounded by a pressurizing medium in the HPP unit. The pressurizing medium may be chilled water or another liquid.
Published U.S. Appl'n. No. 2008/0311259 of Singh et al. deals with egg products placed into a pressurization chamber maintained between 70,000 and 87,000 psi to kill or deactivate undesirable or target pathogens.
U.S. Pat. No. 6,177,115 to Meyer concerns a two-step batch process involving both high pressure and high temperature to achieve sterilization of food having a pH>4.5. This patent illustrates the difficulty associated with inactivation of polyphenol oxidase. Meyer inactivates polyphenol oxidase by de-aerating the product in an initial pre-sterilization process, then pressurizing at 90,000 psi at a temperature of 110° F. to deactivate the enzyme. Sterilization is accomplished by two subsequent elevated temperature pressure cycles. Meyer indicates that high temperature, high pressure treatment is overkill for foods with a pH less than 4.5.
U.S. Pat. No. 6,537,601 to Volson discloses a hydrostatic pressure process, but requires a high temperature in addition to a pressure between 10,000 to 60,000 psi, with the pressure being applied for 1 to 15 minutes.